Expanding on what HJ said, it really depends on where your toilet flange is relative to the finished floor. By design, a toilet flange should be on top of the FINISHED floor, and if it is, pretty much any wax seal you use should work. If it is high or low, you could have issues (high, meaning it is floating in the air, and not properly supported may mean the toilet won't fit at all!; low, you may need a thicker wax ring or to stack a couple). There's one exception - when only using one wax ring, especially on a 3" pipe or an offset flange, do NOT use one with a funnel in it. When pressing it down, that plastic funnel can get squished nearly closed and create all sorts of problems.